Title:Recent Tectonic Activity on Pluto Driven by Phase Changes in the Ice Shell

Abstract: The New Horizons spacecraft has found evidence for geologic activity on the
surface of Pluto, including extensional tectonic deformation of its water ice
bedrock (see Moore et al., 2016). One mechanism that could drive extensional
tectonic activity is global surface expansion due to the partial freezing of an
ocean. We use updated physical properties for Pluto and simulate its thermal
evolution to understand the survival of a possible subsurface ocean. For
thermal conductivities of rock less than 3 W m$^{-1}$ K$^{-1}$, an ocean forms
and at least partially freezes, leading to recent extensional stresses in the
ice shell. In scenarios where the ocean freezes and the ice shell is thicker
than $260$ km, ice II forms and causes global volume contraction. Since there
is no evidence for recent compressional tectonic features, we argue that ice II
has not formed and that Pluto's ocean has likely survived to present day.